A guard band is placed between carriers in wireless communication systems to prevent excessive adjacent channel interference (ACI). In the design of a guard band, difficult and complex ACI scenarios are emphasized, which to be accommodated results in large guard bands and, in a sense, a waste of spectrum. On the other hand, if the guard band is narrow, ACI becomes a problem especially on the edges of the carrier spectrum as illustrated in FIG. 1 by the over-lapping edge portions in which there is a high level of ACI.
The spectral resources in wireless communications systems are assigned to operators in a fixed manner. The scarce spectral resources could be used more efficiently if the assignment to the operators could be made with some flexibility.
Flexible Spectrum Use (FSU) aims at adapting the available spectrum to a network to reflect the changes on the number of subscribers as well as on daily traffic patterns. FSU should enable more versatile operation of the networks, for example, with varying traffic loads in the networks or with some operators providing more focused coverage than others. FSU should provide enough system flexibility towards geographical differences in regulatory spectrum assignments. FSU also aims at easing the deployment of multiple RANs at the launch of the system, even when the spectrum is made available gradually according to increasing traffic demands. Such flexibility may turn out to be of particular importance for the B3G systems requiring wide spectrum bands on frequencies suitable for efficient vehicular communications, that is, below 6 GHz.
Some approaches for flexible spectrum use (FSU) are presented in EU IST WINNER Phase I (IST-2003-507581 WINNER D6.3 WINNER Spectrum Aspects: Assessment report, 2005), and EU IST OverDRiVE projects (IST-2001-35125 OverDRiVE D13 Specification and Performance of Dynamic Spectrum Allocation), both of which are incorporated herein by reference as though fully set forth herein. Further approaches for flexible spectrum use (FSU) are presented in other research projects related to spectrum sharing.
The above referenced approaches for flexible spectrum use (FSU) require either accurate synchronization, coordination between carrier operators or exchanges of full carriers. The requirements of the above referenced approaches for flexible spectrum use (FSU) are frequently problematic, complex and difficult to implement.